1. Field of the Invention
The present invention relates to a method for manufacturing flexible bags and to a vertical type forming, filling and sealing machine for manufacturing the flexible bags from long lengths of film.
2. Description of the Related Art
Conventionally, vertical type forming, filling and sealing machines have been used for putting contents in the form of liquid or paste into bags.
The vertical type forming, filling and sealing machine generally comprises a bag forming guide for forming long lengths of film into tubular shapes, a vertical sealing mechanism for heat sealing mating surfaces at edges of the film formed into tubular shapes along the longitudinal direction of the film to form tubular film, and a horizontal sealing mechanism for heat sealing the tubular film over its entire width. Each of the vertical sealing mechanism and the horizontal sealing mechanism includes a heater bar and a heater receiving bar opposite to each other such that they press and heat the film at the same time to heat seal the opposing inner surfaces of the film.
Contents are supplied into the film below the vertical sealing mechanism and above the horizontal sealing mechanism. While the film is intermittently fed at constant pace, the vertical sealing mechanism heat seals and forms the film into tubular shapes, the contents are supplied thereinto, and then the horizontal sealing mechanism heat seals the film in the width direction, thereby manufacturing flexible bags having the contents enclosed therein.
The flexible bags are successively manufactured in the vertical type forming, filling and sealing machine. Thus, after the horizontal sealing mechanism heat seals the film, the film is cut at the point of the heat sealing in the width direction for division into each bag.
To achieve highly constant amounts of the contents, or to prevent rottenness of the contents due to air present in the flexible bag, the contents may be supplied into the tubular film to a position above the horizontal sealing mechanism and then separated by nipping from the outside the tubular film in which the contents are enclosed.
Especially when the contents are in the form of paste, a pair of squeezing rollers for nipping film from the sides is provided as a mechanism for dividing such contents. The contents in paste form are supplied to a position above the squeezing rollers, and then separated by closing the squeezing rollers. The squeezing rollers in the closed state are rotated to feed the film downward, and a no-filling portion is formed in the area of the film nipped and fed by the squeezing rollers. The no-filling portion is heat sealed by the horizontal sealing mechanism. In this manner, the heat sealing of the film by the horizontal sealing mechanism is favorably performed even for the contents in paste form.
FIGS. 1 to 3 show representative examples of packing with film.
FIG. 1 shows pillow type flexible bag 500. The aforementioned forming, filling and sealing machine is generally used to manufacture pillow type flexible bag 500. Flexible bag 500 includes vertical seal portion 501 which is the portion heat sealed by the vertical sealing mechanism and horizontal seal portions 502 which are the portions heat sealed by the horizontal sealing mechanism.
It is possible to manufacture three-side seal type flexible bag 510 as shown in FIG. 2 by changing the orientation of the horizontal sealing mechanism with respect to the vertical sealing mechanism in the aforementioned forming, filling and sealing machine. Flexible bag 510 also includes vertical seal portion 511 which is the portion heat sealed by the vertical sealing mechanism and horizontal seal portions 512 which are the portions heat sealed by the horizontal sealing mechanism.
In addition, it is possible to manufacture four-side seal type flexible bag 520 as shown in FIG. 3 by providing a second vertical sealing mechanism for the aforementioned forming, filling and sealing machine at the position opposite to the vertical sealing mechanism with the film interposed between them for heat sealing the fold of the film along its longitudinal direction. Flexible bag 520 includes vertical seal portion 523 which is the portion heat sealed by the second vertical sealing mechanism in addition to vertical seal portion 521 and horizontal seal portions 522 similarly to three-side seal type flexible bag 510 shown in FIG. 2.
On the other hand, another form of flexible bags is freestanding bags. Since the freestanding bags such as plastic cases, cans or bottles, can be placed upright on the storefront and fold compact for disposal after the contents thereof are consumed, they have come into widespread use as a packing form replacing the aforementioned ones.
Various forming machines have been proposed to manufacture such freestanding bags, and particularly, Japanese Patent Laid-open Publication No. 11-152104 discloses an apparatus which is an application of the aforementioned vertical type forming, filling and sealing machine. Specifically, the disclosed apparatus has a folding mechanism for folding inward a fold of film at the position opposite to a vertical sealing mechanism with the film interposed between them, and a bottom sealing mechanism for heat sealing two projections of the film formed by folding the film by the folding mechanism to form the bottom of a freestanding bag, added to a forming, filling and sealing machine for manufacturing the aforementioned three-side seal type flexible bag. The forming, filling and sealing machine manufactures freestanding bags in a laid state.
FIG. 4 shows an example of a freestanding bag manufactured by the forming, filling and sealing machine disclosed in Japanese Patent Laid-open Publication No. 11-152104. As shown in FIG. 4, freestanding bag 550 includes two side seal portions 552, top seal portion 551, and bottom seal portion 553. Side seal portions 552 are formed by a horizontal sealing mechanism, top seal portion 551 is formed by the vertical sealing mechanism, and bottom seal portion 553 is formed by the bottom sealing mechanism.
In this manner, the vertical sealing mechanism can be combined with the horizontal sealing mechanism as appropriate to manufacture various forms of flexible bags by using long lengths of film.
In the aforementioned conventional forming, filling and sealing machine, the horizontal sealing mechanism presses and heat seals film with the heater bar and the heater receiving bar as described above. It is necessary to use a heater bar and a heater receiving bar longer than the width of flexible bags to reliably perform heat sealing of the film over the entire width. Flexible bags have various sizes ranging from several centimeters to several tens of centimeters of width depending on the types of contents and the uses of the flexible bags.
As the width of film is greater, the heater bar and the heater receiving bar necessarily press the film in a larger area. An increase in the pressed area of the film means that actual pressure per area applied to the film is reduced as long as the film is subject to the same pressure. As a result, sufficient seal strength cannot be obtained. This is true generally of horizontal seal in the vertical type forming, filling and sealing machine regardless of the form of flexible bags.
Especially when the pillow type flexible bags or freestanding bags are manufactured, film is folded different times in the area of the film heat sealed by the horizontal sealing mechanism. Consequently, a difference in height occurs in the film at the boundary between different thicknesses of the film. The difference in height as well as heat heat sealability or flexibility of the film may cause defective seal at the time of heat sealing by the horizontal sealing mechanism.
Defective seal resulting from such a difference in height is hereinafter described with reference to FIGS. 5a and 5b. FIG. 5a schematically shows a cross section of horizontal seal portion 502 at the time of formation thereof along the width direction of film, together with heater bar 601 and heater receiving bar 602 which constitute part of the horizontal sealing mechanism when pillow type flexible bag 500 shown in FIG. 1 is manufactured. FIG. 5b schematically shows a cross section of side seal portion 552 at the time of formation thereof along the width direction of film, together with heater bar 601 and heater receiving bar 602 which constitute part of the horizontal sealing mechanism when freestanding bag 550 shown in FIG. 4 is manufactured. It should be noted that FIGS. 5a and 5b show the thickness of the film greater than its actual dimension to facilitate understanding of the overlaps of the film.
As shown in FIG. 5a, horizontal seal portion 502 has four thicknesses of the film in the area where vertical seal portion 501 is formed, and two thicknesses of the film in the remaining area. On the other hand, as shown in FIG. 5b, side seal portion 552 has four thicknesses of film in the area where bottom seal portion 553 is formed, and two thicknesses of the film in the remaining area. Silicone rubber 603 is attached to the surface of heater receiving bar 602 opposite to heater bar 601 such that silicone rubber 603 is resiliently deformed with pressure put to the film by heater bar 601 and heater receiving bar 602 to apply force to the entire area in which heat sealing should be performed.
In reality, however, sufficient force may not be applied to cause incomplete heat sealing at the boundaries (areas 610, 611 in FIG. 5a and area 613 in FIG. 5b) between the two thicknesses and the four thicknesses of the film. Such incomplete heat sealing results in leakage of contents to the outside from those boundaries at worst. Particularly, in horizontal seal portion 502 shown in FIG. 5a, a similar problem may also occur in folds 612 of the film.
To prevent the defective seal in the horizontal seal portions caused by an increased size of flexible bags or a difference in height of film as described above, it is contemplated that the horizontal sealing mechanism applies a greater pressure to the film or the film is heated for a longer time period to provide the film with a greater amount of heat.
A greater pressure to the film, however, requires the use of a driving source of a greater output as a driving source for the horizontal sealing mechanism. In connection with this, higher rigidity is needed for the horizontal sealing mechanism including the driving source, which increases the size of the horizontal sealing mechanism including the driving source and thus not preferable. On the other hand, the heating of the film for a longer time period requires a longer time for heat sealing to cause reduced productivity of the flexible bags.
In addition, a greater pressure to the film and the heating of the film for a longer time period mean that the film is caused to be readily sealed. This may bring about defects such as elongation or breakage of the film at the lower end of the heater bar when the film is pressed and heated by the heater bar and the heater receiving bar. The elongation and breakage of the film are phenomena caused by adding the weight of contents to the sealed area of the film in the lower portion of the horizontal sealing mechanism when the horizontal sealing mechanism heat seals the film in the vertical type forming, filling and sealing machine. The elongation or breakage of the film may occur by the pressure itself applied by the horizontal sealing mechanism.
The elongation or breakage of the film at the heat sealing tends to occur when polyethylene film with high heat sealability is used as the film. To prevent the elongation or breakage, flexible bags are generally manufactured by using a laminated film of polyethylene film and nylon film to heat seal the polyethylene films. The use of such a laminated film, however, leads to increased cost of the bag materials.
On the other hand, as the width of flexible bags is greater, the lengths of the heater bar and heater receiving bar of the horizontal sealing mechanism are also greater. When the lengths of the heater bar and heater receiving bar are greater, a slight error of their parallelism causes a difference in applied pressure between one end and the other end of the film in the width direction, resulting in defective seal. Therefore, to maintain the parallelism of the heater bar and the heater receiving bar, it is necessary to improve the accuracy or rigidity of the parts of structures for driving the horizontal sealing mechanism or to provide an additional structure. Consequently, the forming, filling and sealing machine involves an increased manufacturing cost or increased size.
In the forming, filling and sealing machine including squeezing rollers, the squeezing rollers divide contents in film by applying pressure thereto, and the various problems associated with the applied pressure as described above for the horizontal sealing mechanism occur similarly in the squeezing rollers Specifically, a difference in height in film or an increased width of the film partially or generally reduces the pressure applied to the film by the squeezing rollers. As a result, the contents may remain in the area pressurized by the squeezing rollers.
Since the horizontal sealing mechanism heat seals the portion of the film pressed by the squeezing rollers, defective seal may occur if the contents remain in that portion. Even if such a serious problem as defective seal is not produced, the contents remaining in the horizontal seal portion are exposed when the film is cut at the horizontal seal portion for division into each flexible bag, and thus the bag is determined as being nonconforming.
It is an object of the present invention to provide a method for manufacturing flexible bags and a vertical type forming, filling and sealing machine capable of manufacturing flexible bags readily at high speed even when a difference in height which may obstruct heat sealing of film occurs in the area of film where heat sealing is to be performed or even when a wide film is used.
To achieve the aforementioned object, according to the present invention, there is provided a method for manufacturing a flexible bag accommodating contents using long lengths of film while the film is fed downward, the method comprising the steps of heat sealing both edges of the long lengths of film to form tubular film having a vertical seal portion formed by the heat sealing, heat sealing opposing inner surfaces of the tubular film in its width direction except a portion to form an opening, supplying the contents from the opening into the tubular film, and heat sealing opposing inner surfaces of the tubular film in its width direction at the opening after the supply of the contents.
According the method for manufacturing flexible bags of the present invention, the tubular film is heat sealed in the width direction in two separated steps. Specifically, in the first step, the tubular film is heat sealed except a portion to form an opening for supplying contents before the supply of the contents. In the next step, the opening is heat sealed after the supply of the contents. Since the tubular film is heat sealed in the width direction separately before and after the supply of the contents in this manner, the tubular film need not be heated over the entire width after the supply of the contents but may be heated partially. Thus, the tubular film is not elongated by the weight of the contents at the time of its heat sealing in the width direction after the contents are supplied.
In addition, even when the portion of the film to be heat sealed includes a different number of thicknesses of the film in the width direction, it is possible to set optimal heat sealing conditions such as a level or a duration of applied pressure to the tubular film at the time of heat sealing in consideration of the different thicknesses since the heat sealing of the tubular film in the width direction is performed in the two separated steps.
Therefore, the heat sealing of the tubular film in the width direction is favorably performed regardless of the form or size of flexible bags and the material of the film. Moreover, the heat sealing of the tubular film in the width direction separated in two steps can reduce the area to be heat sealed in each step, thereby reducing the time required for the heat sealing.
According to the present invention, there is provided a vertical type forming, filling and sealing machine for manufacturing a flexible bag accommodating contents using long lengths of film while the film is fed downward, the machine comprising a film shaping mechanism for superposing both edges of the long lengths of film to oppose the same surface thereof, a vertical sealing mechanism for heat sealing the superposed edges of the film in its longitudinal direction to form tubular film having a vertical seal portion formed by the heat sealing, a supply nozzle for supplying the contents from above the tubular film into the tubular film, and two horizontal sealing mechanisms for heat sealing opposing inner surfaces of the tubular film in its width direction. A first horizontal sealing mechanism heat seals the tubular film in its width direction except a portion. The supply nozzle has a lower end located below the first horizontal sealing mechanism. A second horizontal sealing mechanism is placed below the first horizontal sealing mechanism. Particularly, the second horizontal sealing mechanism is configured to heat sealed the opposing inner surfaces of the tubular film in its width direction which are not heat sealed by the first horizontal sealing mechanism when the portion heat sealed by the first horizontal sealing mechanism is fed at a position corresponding to the position of the second horizontal sealing mechanism in the feed direction of the tubular film.
As described above, the vertical forming, filling and sealing machine of the present invention includes, as a sealing mechanism for heat sealing the tubular film in the width direction, the first horizontal sealing mechanism for heat sealing the tubular film except a portion in the width direction and the second horizontal sealing mechanism for heat sealing the remaining portion which is not heat sealed by the first horizontal sealing mechanism. The provision of the two horizontal sealing mechanisms eliminates the need of heating the tubular film over the entire width in heat sealing the tubular film in the width direction. This prevents elongation of the tubular film due to the weight of the contents at the time of thermal seal of the tubular film in the width direction.
In addition, since the second horizontal sealing mechanism is placed below the first horizontal sealing mechanism and the supply nozzle for supplying the contents into the tubular film has the lower end placed between the first horizontal sealing mechanism and the second horizontal sealing mechanism, the first horizontal sealing mechanism heat seals the tubular film before the supply of the contents, and as a result, the heat sealing of the tubular film is stably performed by the first horizontal sealing mechanism. With the two separated sealing mechanisms for heat sealing the tubular film in the width direction, each thermal sealing mechanism may be of small size and an additional structure which would be required in a large horizontal sealing mechanism is not needed, and consequently, a smaller size of the entire machine is achieved.
The aforementioned and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the drawings which illustrate several embodiments of the present invention.